Katie Holmes dressed as Jackie O on May 12 in Toronto, where she is filming the miniseries "The Kennedys: After Camelot."Splash News and Pictures (left); Francis Apesteguy/Getty Images (right)

PASADENA, Calif. — Jacqueline Kennedy Onassis was a fashion icon, so it’s no surprise that Katie Holmes looked to her wardrobe for inspiration when portraying her in the Reelz miniseries “The Kennedys: After Camelot.”

The actress found one item particularly useful for getting into the mind of Jackie O.: her Cartier watch.

“She had this very distinct black leather Cartier watch,” Holmes said Friday, at a Television Critics Association press event. “We got a vintage one. There’s something so classic about that and it so embodied her style, understated but elegant. Just putting that on every day, it was of a certain time and I felt that elegance of her.”

Holmes first played the former first lady in the 2011 miniseries “The Kennedys,” which traced the family though 1969, including Bobby Kennedy’s assassination and Jackie’s marriage to Aristotle Onassis. The new four-hour “After Camelot” tracks the next 30 years, from Ted Kennedy’s Chappaquiddick incident to John F. Kennedy Jr.’s plane crash.

“I prepped for six months again to get back into the character. You feel a pressure when you’re doing something you’ve done before, and yet it was a bigger challenge because this series she’s going through so many different things,” Holmes said. “I enjoyed every minute of it because [of] Jackie’s wardrobe. It does help you feel like, ‘OK, she’s coming.’ There’s nothing like Jackie Kennedy’s closet.”

“The Kennedys: After Camelot,” which co-stars Matthew Perry as Ted Kennedy, premieres April 2 on Reelz.